Process for the catalytic cleavage of lactones

ABSTRACT

The present invention relates to a process of cleaving lactones optionally having functional groups to give carboxylic acids, where the corresponding lactone is reacted with hydrogen with catalysis by a compound of a metal of group VIII of the Periodic Table of the Elements which has been modified with organophosphines. The process is preferably carried out in a two-phase system using catalysts which have water-soluble phosphine ligands.  
     The reaction is particularly suitable for cleavage 2-ethylidene-6-hepten-5-olide to give ethylidene-6-heptenecarboxylic acid or isomers thereof. This carboxylic acid can be hydrogenated in a manner known per se to give 2-ethylheptanoic acid.

[0001] The present invention relates to a catalytic process for thepreparation of carboxylic acids by catalytic cleavage of lactones overcatalysts derived from metals of group VIII of the Periodic Table of theElements. In contrast to the known cleavage of lactones bysaporification, in which carboxylic acids having hydroxyl groupsoriginating from the lactone group, or functions formed from these form,in the cleavage according to the invention a carboxyl function is formedfrom the lactone function present in the molecule, although no hydroxylfunction or functional group derived therefrom is formed.

[0002] Lactones play an important role, for example, in the fragranceand flavor industry. By contrast, as a starting material for thepreparation of other products, lactones have hitherto only appeared to aminor degree. This is due, firstly, to the reactivity of the lactones.In the simplest reaction of lactones, hydrolysis, hydroxycarboxylicacids or derivatives thereof are formed. It is generally necessary toreduce the hydroxyl function; firstly to provide carboxylic acids oralso esters with a broad potential field of use, and secondly, ofcourse, also to avoid the back-formation of lactone. The otherwise knownreactions of lactones virtually always lead only to products which areof no or only low industrial importance and/or can be prepared morefavorably by another method.

[0003] It is also a factor here that, in addition to the frequentlyundesired reactivity pattern, lactones are generally expensive products.This is due to the comparatively complex preparation process. Of theprocesses for lactone preparation, the telomerization of butadiene withCO₂ and optionally further starting material compounds has recentlybecome the focal point. As the starting materials are low in cost andpresent in large amounts, some lactones at least have become accessibleat low cost and are available as starting substances for secondaryreactions, some of which have still to be developed, to give productswhich are of potential interest for certain fields of application.

[0004] One example of a readily accessible lactone which may bementioned is the δ-lactone 2-ethylidene-6-heptenolide, which is preparedin a telomerization reaction from two molecules of butadiene and onemolecule of CO₂. Organophosphine-modified palladium complexes are usedas catalysts. The process can be modified in various ways. Using modemprocess variants, yields of 95% with regard to the lactone are possible,and even the problem of catalyst recycling has meanwhile been solved ina number of ways. According to the process disclosed in WO 98/57745,this is possible, for example, by immobilizing the catalyst on apolystyrene support, or by extracting the resulting lactone when thereaction is complete and returning the catalyst which is insoluble inthe extractant. This last process is disclosed inChemie-Ingenieur-Technik 72 (2000), pages 58 to 61.

[0005] Hitherto known secondary reactions which have been carried out onthis lactone are alkaline cleavage, which produces, as product,2-ethylidene-5-hydroxy-6-heptonic heptenoic acid, and acid-catalyzedcleavage in the presence of methanol, which produces a mixture of themethoxy derivatives and the methylester of the abovementioned acid, seeZ. Chem. 25 (1985), pages 220 to 221. Also known is the synthesis of thecorresponding γ-lactone from 2-ethylidene-6-heptenolide.

[0006] It is an object of the present invention to provide a processwith which lactone cleavages can be carried out which produce, assecondary products, carboxylic acids which do not have hydroxyl groupsor substituents derived therefrom. The process should be easy to carryout, produce high yields and leave intact other functional groupspresent on the lactone, such as, for example, olefin functions.

[0007] We have found that this object is achieved by a process forcleaving lactones optionally having functional groups to give carboxylicacids, this process comprising reacting the corresponding lactone withhydrogen under catalysis by a compound of a metal of group VIII of thePeriodic Table of the Elements which has been modified withorganophosphines.

[0008] The process according to the invention permits, as a result ofthe cleavage of lactones, the preparation of carboxylic acids which nolonger have hydroxyl groups originating from the lactone function, butin which other functional groups are generally still present.

[0009] This is a transition-metal-catalyzed process in whichcatalytically active complexes of metals of group VIII of the PeriodicTable of the Elements which have been modified with phosphine ligandsare used. The metals are preferably chosen from the group consisting ofRu, Os, Pd, Pt, Rh and Ir. In particular, the metals are chosen from thegroup consisting of Rh and Ir.

[0010] The type of phosphine ligands which are used varies depending onthe method by which the process according to the invention is carriedout. This process can be carried out homogeneously in an organic phase,optionally with the addition of a solvent, heterogeneously in organicphase using an insoluble catalyst fixed to a support, optionally withthe addition of an organic solvent, or in a two-phase system having oneaqueous phase and one organic phase, optionally with the addition of anorganic solvent.

[0011] If the homogeneous reaction method is chosen, the customaryorganophosphines are generally suitable; these may be mono-, bi- or elsepolydentate. In general, mono- or bidentate phosphines are used. Thesemay be chosen from the known organophosphines soluble in the customarysolvents. These are, for example, triarylphosphines, trialkylphosphinesand alkylene- and arylene-bridged diphosphines which carry alkyl or arylsubstituents. Examples include trimethylphosphine,triisopropylphosphine, tricyclohexylphosphine, triphenylphosphine,diphenylphosphinoethane and -methane, dimethylphosphinoethane and-methane, and the phosphines known under the name BINAP.

[0012] If the abovementioned phosphines are used, the reaction iscarried out without the addition of a solvent or with the addition of acustomary solvent, for example heptane, toluene, diethyl ether, dioxaneor methanol or else mixtures thereof.

[0013] The resulting carboxylic acid is isolated by, for example,removing it from the reaction mixture by distillation, or extracting ittherefrom, for example by acid-base extraction or using a suitablesolvent.

[0014] Simple isolation and separation of the product from the catalystis, according to one variant of the present invention, possible usingphosphine ligands fixed to supports. All of the abovementioned phosphineligands suitable for use in the process according to the invention canbe fixed to suitable supports. These are, firstly, organic polymers, forexample polystyrene, which may optionally be modified (Merrifield resin,Wang resin, aminomethyl-substituted polystyrene), Tentagel and polyamideresins. It is also possible to use inorganic supports, such as silicondioxide and pulp.

[0015] In this process variant in which organophosphines fixed tosupports are used, the reaction mixture can, when the reaction iscomplete, be separated off simply by decantation from the catalyst,which can then be reintroduced into the reaction. The reaction mixtureseparated off from the catalyst is then isolated and purified usingcustomary methods, for example removal of the solvent by distillationfollowed by purification of the product by distillation.

[0016] In a preferred embodiment of the present invention, the processis carried out in a water/organic solvent two-phase system, in whichcase water-soluble phosphine ligands are used. These phosphine ligandsmay be mono- or bidentate and have the customary organic groups known toa person skilled in the art on the organic substituents bonded to thephosphorous, as a result of which the solubility in water is effected.Examples of such groups which effect solubility in water includecarboxyl functions, hydroxyl functions, alkoxylated hydroxyl functions,phosphonato functions and sulfonyl functions, preferably sulfonylfunctions.

[0017] One group of suitable water-soluble phosphine ligands are thetriarylphosphines corresponding to the formula (I) below

[0018] in which Ar is a phenyl or naphthyl radical, M1, M2 and M3,independently of one another, are an alkali metal ion, an optionallyorganosubstituted ammonium ion, an alkaline earth metal ion or a zincion and are present in the stoichiometrically required amount, and x, yand z are identical or different and independently of one another are 0or 1.

[0019] Preferably, in formula (I), x, y and z are 1, and Ar is a phenylradical. In particular, trisodium tri(n-sulfonyl)phosphine (TPPTS) isused as ligand according to formula (I).

[0020] Another group of suitable substituents corresponds to theformulae (IIa) or (IIb)

[0021] in which M1 to M6 or M1 to M8, respectively, independently of oneanother are an alkali metal ion, an optionally organosubstitutedammonium ion, an alkaline earth metal ion or a zinc ion, and are presentin the stoichiometrically required amounts, and a-f and a-h,respectively, independently of one another are 0 or 1.

[0022] Preferred phosphines of the formula (IIa) are those in which 3 to6 sulfonyl groups SO₃M are present; preferred phosphines according tothe formula (IIb) have 4 to 8 sulfonyl groups. Of the phosphinescorresponding to the formulae (IIa) and (IIb), particular preference isgiven to the ligands known under the name BISBIS and BINAS.

[0023] If the reaction is carried out in a two-phase system, an organicsolvent may be present, but the reaction may also be carried out in theabsence of a solvent. Examples of suitable organic solvents includenonpolar solvents, such as paraffins, aromatic solvents, for exampletoluene and xylene, ethers, such as, for example, diethyl ether andmethyl tert-butyl ether, acetonitrile and chlorinated hydrocarbons, suchas, for example, dichloromethane and chloroform.

[0024] The catalytically active catalyst complex is prepared bygenerally known methods, generally by mixing a suitable precursorcompound with the respective phosphine ligands in the required amounts.Suitable precursor compounds are known to the person skilled in the art.Suitable rhodium precursor compounds include, for example, RhCl₃.3H₂O,[Rh(COD)Cl]₂(COD=1,5-cyclooctadiene) and Rh(CH₃COO)₃ and other compoundsknown to the person skilled in the art.

[0025] Examples of suitable iridium precursor compounds which may bementioned are IrCl₆ ³⁻,IrCl₃.nH₂O and H₂[IrCl₆].nH₂O.

[0026] The phosphine ligands used in the process according to theinvention are used in all process variants in relative amounts withregard to the rhodium or iridium metal which are at values of from 1:3to 1:1000, preferably 1:10 to 1:100. The catalyst is used in an amountwhich is at values of from 100 to 10000, preferably 500 to 10000, mol oflactone/mol of metal ion.

[0027] In the preferred process variant according to the presentinvention, in which the water-soluble phosphines (I), (IIa) or (IIb) areused, the metal/phosphine ligand ratio is 1:3 to 1:1000, preferably 10to 100. The aqueous phase comprises here 20 to 5000 ppm of metal ion,preferably 250 to 1500 ppm. The relative amount of metal ions which isused is 1·10⁻⁵ to 1·10⁻² mol of metal ion/mol of lactone. The aqueousphase comprises here 1 to 25% by weight, preferably 2.5 to 15% byweight, of phosphine ligand.

[0028] The process according to the invention is carried out in allprocess variants at temperatures of from 50 to 200° C. If functionalgroups are present on the lactone, the temperature is preferably 50 to150° C., in particular 70 to 130° C., and the process is carried outunder a hydrogen atmosphere at pressures of from 1 to 150 bar,preferably 1 to 30 bar.

[0029] The product mixture obtained following cleavage of the lactoneand which has the carboxylic acids formed is separated from the solutionwhich comprises the catalytically active metal complex or the phosphineligands. In the case of a homogeneous reaction method in the organicphase, this is achieved by distilling off the solvent and distilling theresidue containing the product, optionally following oxidation of thephosphine ligands or converting them into a phosphonium salt. If animmobilized ligand is used, the product solution is removed from this bydecantation and subsequently worked up in an appropriate manner.

[0030] If the process is carried out as a two-phase reaction, thework-up comprises, firstly, simply separating off the organic phasewhich contains the product from the aqueous phase. The carboxylic acidis then purified by the known methods, conventionally by distillation.The aqueous catalyst solution can then be reused.

[0031] The process of lactone cleavage according to the invention can beused widely and is suitable both for γ-lactone and for δ-lactone. It ispossible to use lactones which have different substituents on their ringsystem or else themselves have a double bond in the ring. Examples offunctional groups which can have the lactone substrate include olefinicdouble bonds and acetylenic triple bonds, carboxyl functions, carbonylfunctions, hydroxyl functions, epoxide functions, nitrile groups, aminogroups, nitro groups, in particular olefinic double bonds.

[0032] Depending on the reaction conditions chosen a double-bondisomerization can be observed. Nonobservance of the respective reactionconditions required for the reaction to proceed gently to attain onlythe desired lactone cleavage, may also lead to the observance of a moreor less complete hydrogenation of the functional groups, such as, forexample, of the olefinic double bonds.

[0033] As already mentioned, one of the advantages of the processaccording to the invention is that functional groups are retained duringthe lactone cleavage. In particular, the process of lactone cleavageaccording to the invention can be readily carried out such that noolefinic double bonds are hydrogenated. The process is thereforesuitable in particular for the cleavage of lactones which have olefinicdouble bonds on the substituents or an olefinic double bond in the ringitself.

[0034] The process of lactone cleavage according to the invention isparticularly suitable for converting 2-ethylidene-6-hepten-5-olide into2-ethylidene-6-heptenoic acid or isomers thereof. Here, it is possibleto achieve conversions of 100% and selectivities for the2-ethylidene-6-heptenoic acid or for double-bond isomers which form as aresult of rearrangement reactions of up to 100%.

[0035] The present application also refers to a process for thepreparation of 2-ethylheptanoic acids by cleavage of2-ethylidene-6-hepten-5-olide and hydrogenation of the resulting2-ethylidene-6-heptenecarboxylic acid or isomers thereof.2-Ethylheptanoic acid is an interesting alternative to 2-ethylhexanoicacid. The latter is used as a starting material for lubricants,plasticizers and alkyd resins. The acid is used here, depending on theintended use, in the form of its esters, metal salts or the acid itself.The acid is frequently also converted to the corresponding alcohol byhydrogenation, which alcohol is esterified with certain carboxylic acidsand then used as plasticizer.

[0036] However, in view of the preparation aspects, 2-ethylheptanoicacid is advantageous since it can be prepared from two C₄ buildingblocks and one C₁ building block (butadiene and CO₂ respectively). Dueto the uneven number of carbons, this is not the case for2-ethylhexanoic acid, and recourse has to be made to propene for itspreparation. However, propene is a raw material in short supply comparedwith butadiene, meaning that it is desirable to be able to use thelatter as a raw material.

[0037] 2-Ethylheptanoic acid as a C₉ acid is known per se. It hasproperties which predestine it as replacement for 2-ethylhexanoic acidwhich has hitherto been used on a large scale. However, despite thenumber of carbon atoms which is favorable per se, it has not hithertobeen possible to prepare 2-ethylheptanoic acid in a manner which iscost-effective and which permits synthesis on an industrial scale.

[0038] It was a further object of the present invention to provide aprocess with which 2-ethylheptanoic acid can be prepared simply,cost-effectively and in high yields. The process should in addition beable to be operated on an industrial scale.

[0039] This object is achieved by a process for the preparation of2-ethylheptanoic acids, which comprises the above-described catalyticcleavage of 2-ethylidene-6-hepten-5-olide to give2-ethylidene-6-heptenoic acids and isomers thereof and the hydrogenationof this carboxylic acid or of the resulting isomer mixture.

[0040] According to one embodiment of the present invention, the lactonecleavage and the hydrogenation of the olefinic double bond can becarried out in a single process step. Here, the catalyst used in thelactone cleavage is chosen and the reaction conditions are adjusted suchthat the reaction is not complete following cleavage of the lactonering, but the olefinic double bonds in the substrate are likewisehydrogenated. This hydrogenation can be achieved, in particular, usingsevere reaction conditions, for example temperatures of >125° C. andpressures of >10 bar. According to another preferred embodiment of thepresent invention, the hydrogenation is carried out using a customarycatalyst system known per se over the ethylidene-heptenecarboxylic acidisomer mixture, formed following lactone cleavage, which has been freedfrom the catalyst system used.

[0041] The hydrogenation is carried out using the suitable catalystcompounds known to a person skilled in the art, it being possible forthe hydrogenation to be carried out homogeneously or heterogeneously.The hydrogenation is preferably carried out under heterogeneousconditions. In this heterogeneous method, it is preferred to use, ascatalyst, metals chosen from the group consisting of nickel, palladiumand platinum. Mixtures of these preferred metals can also be used. Thecatalyst metals or mixtures thereof can be used without supportmaterial. If a support material is used, then it consists of thecustomary materials known to a person skilled in the art, for exampleactivated carbon, Al₂O₃, SiO₂, ZrO₂ and MgO, preferably activated carbonor Al₂O₃.

[0042] During the hydrogenation of the ethylidene-heptanecarboxylicacids, it is possible for an organic solvent to be present. Examples ofsuitable organic solvents include lower alcohols, paraffins, ethers. Thereaction can, however, also be carried out in the absence of a solvent.The chosen temperatures are from 0 to 300° C., preferably 40 to 220° C.,and the pressures are from 1 to 300 bar, preferably 5 to 15 bar.

[0043] In this way, complete hydrogenation of the olefinic double bondof the ethylideneheptenoic acids used can be achieved.

[0044] The application is now described in more detail in the examplesbelow.

EXAMPLES Cleavage of the Lactone Ring

[0045] 1. Procedure in an Autoclave with V=67 ml

[0046] The investigations for the cleavage of the lactone ring werecarried out in an autoclave with a volume of 67 ml. The reactionsolution consisted of two imiscible phases: the aqueous catalyst phasecontaining RhCl₃ as catalyst metal and TPPTS as ligand. The organicphase consisted either of a nonpolar solvent and the starting material,the δ-lactone, or only of the δ-lactone. The volume of the phases was 15ml in each case. The reactor was provided with an immersion tube whichpermitted sampling from the organic phase. The two phases were mixedusing a disc stirrer.

[0047] The reactor was evacuated prior to the start of the reaction andthe reaction solution was sucked in using the resulting vacuum. Themixture was then heated to the reaction temperature with slow stirring,the stirrer was switched off, hydrogen was injected to the desiredpressure and the reaction was started by switching on the stirrer.

[0048] Samples were taken after 5, 10, 15, 30 and 60 min. Analysis wascarried out using a HP® 6890 GC-FID.

[0049] The results of the experiments with the 67 ml-autoclave aresummarized in Table 1. The initial weights of lactone and water were 15g in each case, giving a mass ratio of organic phase to aqueous phase of1:1.

[0050] The column “Lactone in mol % after t=5 min” gives the molarpercentage of the δ-lactone in the autoclave after a reaction time of 5minutes. The column “Time t in min at convertion=1” gives the samplingtime point at which δ-lactone could no longer be detected in theautoclave. TABLE 1 Hydrogenation of δ-lactone usingrhodium/triarylphosphine Lactone in Time t in min P/Rh in Stirrer speedPressure p of mol % after t = 5 Temperature in at conver- ExperimentLigand Rh/lactone ppm mol/mol in rpm H₂ in bar min ° C. sion = 1 LC4TPPTS 1000 10 1000 30 35 90 15 LC5 TPPTS 1000 10 1000 10 26 90 60 LC6TPPTS 1000 10 1000 20 18 90 15 LC7 TPPTS 1000 10 1000 10 56 90 30 LC8TPPTS 1000 10 1000 10 69 80 60 LC9 TPPTS 1000 10 1000 10 28 100 15 LC10TPPTS 1000 10 1000 20 45 90 15 LC12 TPPTS 500 10 1000 10 44 90 15 LC13TPPTS 1500 10 1000 10 15 90 30 LC14 TPPTS 250 10 1000 10 80 90 60 LC15TPPTS 1500 10 1000 10 18 90 10 LC16 TPPTS 500 10 1000 10 42 90 30 LC17TPPTS 1000 10 1000 10 63 90 30 LC18 TPPTS 1000 10 1000 10 60 90 15 LC19TPPTS 1000 10 800 10 56 90 30 LC20 TPPTS 1000 10 1200 10 25 90 15 LC21TPPTS 1000 5 1000 10 63 90 60 LC22 TPPTS 1000 10 1200 10 24 90 15 LC23TPPTS 1000 20 1000 10 31 90 15 LC24 TPPTS 1000 10 600 10 60 90 30 LC25TPPTS 500 10 1000 10 44 90 15 LC26 BINAS 500 10 1000 10 64 90 60 LC27BISBIS 500 10 1000 10 77 90 60

[0051] Some of the experiments summarized in the table are described inmore detail below by way of example.

Example 1.1 (Experiment LC8)

[0052] The reaction solution consisting of 15.0 g of δ-lactone, 12.5 gof water, 38 mg of RhCl₃*3H₂O and 2.8 ml of 25% strength TPPTS solutionis prepared in a Schlenk vessel.

[0053] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 80° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 10 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹.

[0054] Sampling takes place after 5, 10, 15, 30 and 60 min, one minutebeing waited in each case after the stirrer has been switched off toallow separation of the phases. TABLE 2 Example 1.1 Time t Lactone n(Lactone) in min in mol % in mol TON TOF in h⁻¹  0 98.55 0.10  0   0  569.04 0.07 204 2453 10 47.87 0.05 351 2106 15 19.00 0.02 551 2204 30 6.88 0.01 635 1270 30  0.00 0.00 683  683

Example 1.2 (Experiment LC22)

[0055] The reaction solution consisting of 15.0 g of δ-lactone, 12.2 gof water, 39 mg of RhCl₃*3H₂O and 2.8 ml of 25% strength TPPTS solutionis prepared in a Schlenk vessel.

[0056] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 90° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 10 bar and thereaction is started by accelerating the stirrer to 1200 min⁻¹.

[0057] Sampling takes place after 5, 10, 15 and 30 min, one minute beingwaited in each case after the stirrer has been switched off to allowseparation of the phases. TABLE 3 Example 1.2 Time t Lactone n (Lactone)in min in mol % in mol TON TOF in h⁻¹  0 100.00 0.10  0   0  5  23.890.02 530 6363 10  5.53 0.01 658 3947 15  0.00 0   696 2785 30  0.00 0  696 1393

Example 1.3 (Experiment LC4)

[0058] The reaction solution consisting of 15.0 g of δ-lactone, 12.2 gof water, 39 mg of RhCl₃*3H₂O and 2.8 ml of 25% strength TPPTS solutionis prepared in a Schlenk vessel.

[0059] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 90° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 30 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹.

[0060] Sampling takes place after 5, 10 and 15 min, one minute beingwaited in each case after the stirrer has been switched off to allowseparation of the phases. TABLE 4 Example 1.3 Time t Lactone n (Lactone)In min in mol % in mol TON TOF in h⁻¹  0 96.82 0.10  0   0  5 34.82 0.03431 5173 10  6.79 0.01 626 3756 15  0.00 0.00 673 2693

Example 1.4 (Experiment LC12)

[0061] The reaction solution consisting of 15.0 g of δ-lactone, 13.6 gof water, 19 mg of RhCl₃*3H₂O and 1.4 ml of 25% strength TPPTS solutionis prepared in a Schlenk vessel.

[0062] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 90° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 10 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹.

[0063] Sampling takes place after 5, 10 and 15 min, one minute beingwaited in each case after the stirrer has been switched off to allowseparation of the phases. TABLE 5 Example 1.4 Time t Lactone n (Lactone)in min in mol % in mol TON TOF in h⁻¹  0 96.80 0.10   0   0  5 44.020.04  732 8784 10 10.92 0.01 1191 7147 15  0.00 0.00 1343 5370

Example 1.5 (Not Listed in Table 1)

[0064] The reaction solution consisting of 5.0 g of δ-lactone, 6.8 g ofn-heptane, 14.06 g of water, 13 mg of RhCl₃*3H₂O and 1.1 ml of 25%strength TPPTS solution is prepared in a Schlenk vessel.

[0065] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 90° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 10 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹.

[0066] After 60 min, the stirrer is switched off, the phases areseparated and the organic phase is analyzed. The δ-lactone was cleavedcompletely into the unsaturated 2-ethylideneheptenoic acids.

Example 1.6 (Not Listed in Table 1)

[0067] The reaction solution consisting of 5.0 g of δ-lactone, 15 g oftoluene, 13.3 g of water, 0.24 mg of [Rh(COD)Cl]₂ and 1.7 ml of 25%strength TPPTS solution is prepared in a Schlenk vessel.

[0068] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 70° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 30 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹.

[0069] After 3.5 h, 95% conversion of the δ-lactone is observed, whichwere converted exclusively to the isomeric 2-ethylideneheptenoic acids.

[0070] 2 Procedure in an Autoclave with V=300 ml

Example 2.1

[0071] Adiabatic Reaction Method with Recycling of the Catalyst solution

[0072] The reaction solution consisting of 75.0 g of δ-lactone, 60.8 gof water, 188 mg of RhCl₃*3H₂O (1000 ppm) and 16.6 ml of 25% strengthTPPTS solution is prepared in a Schlenk vessel.

[0073] The 300 ml reactor is evacuated and the reaction solution issucked in. The mixture is then heated to 90° C. with slow stirring, thestirrer is switched off, hydrogen is injected to a pressure of 10 barand the reaction is started by accelerating the stirrer to 1000 min⁻¹.

[0074] Sampling takes place after 5, 10, 15, 20 and 25 min, one minutebeing waited in each case after the stirrer has been switched off inorder to permit separation of the phases. After 30 min, the hydrogen isreleased and the reaction solution is transferred by means of a streamof argon into a separating funnel purged with argon. The phases areseparated, and the organic phase is analyzed by means of gaschromatography. The water content of the organic phase is determined bytitration. The emptied reactor is evacuated, and the aqueous catalystphase used is sucked in again. 75.1 g of δ-lactone are introduced into aSchlenk vessel purged with argon and sucked to the catalyst in thereactor. The catalyst phase is used a total of five times. A mixture ofisomeric 2-ethylideneheptenoic acids forms, partial hydrogenation of theolefinic double bonds also being observed. TABLE 6 Example 2.1 Use ofInitial weight δ-Lactone Water content Max. catalyst of δ-lactoneconversion of the organic temperature phase in g in % phase in % in ° C.1 75.0  92 0.8  96 2 75.1 100 0.6 122 3 75.1 100 0.8 131 4 75.2 100 0.8122 5 75.2 100 1.0 119

Example 2.2

[0075] Isothermal Method with Recycling of the Catalyst Solution

[0076] The reaction was carried out as described in Example 2.1, thereactor being provided with a U-tube, through which cooling water ispassed in order to dissipate the heat of reaction liberated.

[0077] The reaction solution consisting of 75.0 g of δ-lactone, 60.8 gof water, 94 mg of RhCl₃*3H₂O (500 ppm) and 16.6 mg of 25% strengthTPPTS solution is prepared in a Schlenk vessel.

[0078] The reactor is evacuated and the reaction solution is sucked in.The mixture is then heated to 110° C. with slow stirring, the stirrer isswitched off, hydrogen is injected to a pressure of 10 bar and thereaction is started by accelerating the stirrer to 1000 min⁻¹. After 30min, the hydrogen is released and the reaction solution is transferredby means of a stream of argon into a separating funnel purged withargon. The phases are separated and the organic phase is analyzed bymeans of gas chromatography. The water content of the organic phase isdetermined by titration. The emptied reactor is evacuated and theaqueous catalyst phase used is sucked in again. 75.1 g of δ-lactone areintroduced into a Schlenk vessel purged with argon and sucked to thecatalyst in the reactor. A total of six experiments are carried outusing the same catalyst phase. Deactivation, like hydrogenation of theolefinic double bonds, is not observed. TABLE 7 Example 2.2 Initialweight δ-Lactone Water Max. Experiment of δ-lactone conversion contenttemperature No. in g in % in % in ° C. 1 75.4  78 2.2  110 ± 2 2 75.1100 0.74 110 ± 2 3 75.0 100 0.67 110 ± 2 4 75.2 100 0.66 110 ± 2 5 75.5100 0.81 110 ± 2 6 75.1 100 0.96 110 ± 2

[0079] Purification of the 2-Ethylideneheptenoic Acid

[0080] The isomeric 2-ethylideneheptenoic acids accessible by cleavageof δ-lactone are distilled in order to remove traces of water whichremain in the product. At a pressure of p=2*10⁻² mbar and a temperatureof 30° C., the water is removed, and as the temperature of the bath isincreased to 110° C. (head temperature 75° C.), the product is obtainedas distillate.

[0081] Hydrogenation of the 2-Ethylideneheptenoic Acid

[0082] The remaining olefinic double bonds of 2-ethylideneheptenoic acidare hydrogenated using a heterogeneous hydrogenation catalyst.

Example 4.1

[0083] 0.5 g of palladium on activated carbon (5% Pd) is weighed into a300 ml autoclave. The reaction solution consisting of 10.0 g of2-ethylideneheptenoic acid and 90 ml of methanol is prepared under argonand sucked into the autoclave which has been evacuated beforehand. Themixture is then heated to 60° C., hydrogen is injected to a pressure of10 bar and the reaction is started by accelerating the stirrer is 700min⁻¹. After a reaction time of five minutes, the starting material iscompletely consumed, 2-ethylheptanoic acid forming as the sole product.

Example 4.2

[0084] The process is carried out as described in Example 4.1 using 90ml of n-heptane instead of the methanol. After 30 min, the yield is 100%2-ethylheptanoic acid.

Example 4.3

[0085] The process is carried out as described in Example 4.1 using 10 gof Al₂O₃ balls (2-4 mm) containing 0.5% palladium as catalyst. After 60min, the yield is 100% 2-ethylheptanoic acid.

Example 4.4

[0086] The process is carried out as described in Example 4.3, using 5 gof palladium on activated carbon granules (1 mm) containing 1% palladiumas catalyst. After 30 min, the conversion is 95%, 2-ethylheptanoic acidbeing formed exclusively.

Example 4.5

[0087] 0.5 g of palladium on activated carbon (5% Pd) is weighed into a300 ml autoclave. 68.8 g of 2-ethylidencheptenoic acid are sucked intothe autoclave which has been evacuated beforehand. The mixture is thenheated to 60° C., hydrogen is injected to a pressure of 30 bar and thereaction is started by accelerating the stirrer to 1000 rpm. After 6hours, the conversion is 86%, 2-ethylheptanoic acid being formedexclusively.

Example 4.6

[0088] 2.5 g of palladium on activated carbon (5% Pd) is weighed into a300 ml autoclave. 50 g of 2-ethylideneheptenoic acid are sucked into theautoclave which has been evacuated beforehand. The mixture is thenheated to 190° C., hydrogen is injected to a pressure of 15 bar and thereaction is started by accelerating the stirrer to 700 min⁻¹. After 90min, the conversion is 80%, 2-ethylheptanoic acid being formedexclusively.

We claim:
 1. A process for the cleavage of lactones optionally having functional groups to give carboxylic acids, which comprises reacting the corresponding lactone with hydrogen under catalysis by a compound of a metal of group VIII of the Periodic Table of the Elements, preferably from the group consisting of Ru, Os, Pd, Pt, Rh and Ir, in particular a rhodium or iridium compound which has been modified with organophosphines.
 2. A process as claimed in claim 1, wherein the process is carried out homogeneously and optionally with the addition of a solvent, heterogeneously in the organic phase using an insoluble catalyst fixed to a support and optionally with the addition of an organic solvent, or in a two-phase system with one aqueous phase and one organic phase and optionally with the addition of an organic solvent.
 3. A process as claimed in claim 2, wherein the process is carried out in the organic phase and mono- or bidentate phosphines, preferably trialkylphosphines, triarylphosphines, alkylene- or arylene-bridged diphosphines having alkyl or aryl substitutents, in particular trimethylphosphine, triisopropylphosphine, tricyclohexylphosphine, triphenylphosphine, diphenylphosphinoethane, diphenylphosphinomethane, dimethylphosphinoethane, dimethylphosphinoethane or BINAP are used.
 4. A process as claimed in claim 2, wherein the reaction is carried out heterogeneously in the organic phase using a phosphine which is fixed to an organic support, preferably optionally modified polystyrene, Merrifield resin, Wang resin, aminomethyl-substituted polystyrene, Tentagel or polyamide resins, or to inorganic supports, preferably silicon dioxide or pulp.
 5. A process as claimed in claim 2, wherein the reaction is carried out in a two-phase system having an aqueous phase and an organic phase using a mono- or bidentate water-soluble phosphine, preferably a phosphine which has at least one carboxyl function, hydroxyl function, alkoxylated hydroxyl function, phosphonato function or sulfonyl function, in particular a phosphine having at least one sulfonyl group, preferably triarylphosphines of the formula (I)

in which Ar is a phenyl or naphthyl radical, in particular a phenyl radical, M1, M2 and M3, independently of one another, are an alkali metal ion, an optionally organo-substituted ammonium ion, an alkaline earth metal ion or a zinc ion and are present in the stoichiometrically required amount, and x, y and z are identical or different and independently of one another are 0 or 1, or of the formulae (IIa) or (IIb),

in which M1 to M6 or M1 to M8, respectively, independently of one another are an alkali metal ion, an optionally organo-substituted ammonium ion, an alkaline earth metal ion or a zinc ion and are present in the stoichiometrically required amounts, and a-f and a-h, respectively, independently of one another are 0 or 1, in particular a phosphine of the formula (IIa) which has 3 to 6 sulfonyl groups, or of the formula (IIb) which has 4 to 8 sulfonyl groups.
 6. A process as claimed in claim 5, wherein a phosphine is used which is chosen from the group consisting of the phosphines known under the names TPPTS, BISBIS and BISNAS.
 7. A process as claimed in any of claims 1 to 6, wherein the catalytically active complex is prepared by mixing a suitable precursor compound with the corresponding phosphine ligands in the required amounts, preferably from RhCl₃.3H₂O, [Rh(COD)Cl]₂, or Rh(CH₃COO)₃ and IrCl₆ ³⁻, IrCl₃.nH₂O or H₂[IrCl₆].nH₂O.
 8. A process as claimed in any of claims 1 to 7, wherein the phosphine ligands are used, with regard to the rhodium and iridium metal, in relative amounts of from 1:3 to 1:1000, preferably 10 to 100, and the catalyst is used in an amount of from 100 to 10 000 mol, preferably 500 to 10 000 mol, of lactone/mol of metal ion.
 9. A process as claimed in any of claims 1 to 8, wherein a phosphine corresponding to one of the formulae (I), (IIa) or (IIb) is used and the metal/phosphine ligand ratio is 1:3 to 1:1000, preferably 10 to 100, and the aqueous phase comprises 20 to 1000 ppm of metal ion, preferably 250 to 1500 ppm of metal ion.
 10. A process as claimed in claim 9, wherein the relative amount of metal ions used is 2·10⁻⁶ to 5·10⁻² mol of metal ions/mol of lactone, and the aqueous phase comprises 1 to 25% by weight, preferably 2.5 to 15% by weight, of phosphine ligand.
 11. A process as claimed in any of claims 1 to 10, wherein the process is carried out at temperatures of from 50 to 200° C., preferably 50 to 150° C., in particular 70 to 130° C. and at hydrogen pressures of from 1 to 150 bar, preferably 1 to 30 bar.
 12. A process as claimed in any of claims 1 to 11, wherein the lactone is chosen from the group consisting of γ- and δ-lactones which optionally have functional groups and/or a double bond in the ring, preferably have, as functional groups, one or more functions which independently of one another are chosen from the group consisting of olefinic double bonds, acetylenic triple bonds, carboxyl functions, carbonyl functions, hydroxyl functions, epoxide functions, nitrile groups, amino groups and nitro groups, in particular olefinic double bonds.
 13. A process as claimed in any of claims 1 to 12, wherein the lactone used is 2-ethylidene-6-hepten-5-olide.
 14. A process as claimed in claim 13, wherein 2-ethyidene-6-heptenoic acid and/or one or more isomers of this acid form.
 15. A process for the preparation of 2-ethylheptanoic acid, which comprises cleavage and hydrogenation of 2-ethylidene-6-hepten-5-olide by the process as claimed in one of claims 1 to 14 to give 2-ethylidene-6-heptenoic acid and/or one or more isomers thereof.
 16. A process as claimed in claim 15, wherein the ring cleavage and the hydrogenation are carried out in one process step.
 17. A process as claimed in claim 15, wherein the hydrogenation is carried out following cleavage of the lactone and isolation of the resulting product from the catalyst solution used therein in a manner known per se in a homogeneously or heterogeneously catalyzed reaction method.
 18. A process as claimed in claim 17, wherein the hydrogenation is carried out heterogenously over catalysts chosen from the group consisting in nickel, palladium and platinum and mixtures of these metals.
 19. A process as claimed in claim 17, wherein the catalyst is used without support material, or is applied to a support material chosen from the group consisting of activated carbon, Al₂O₃, SiO₂, ZrO₂ and MgO, preferably activated carbon or Al₂O₃.
 20. A process as claimed in any of claims 15 to 19, wherein the reaction is carried out at temperatures of from 0 to 300° C., preferably from 40 to 220° C., and pressures from 1 to 300 bar, preferably from 5 to 15 bar. 